1. Field of the Invention
The present invention relates to a measuring apparatus and an exposure device.
2. Description of the Related Art
A surface position measuring apparatus for detecting a position of a front surface of a substrate is described by an example of an exposure device.
An exposure device projects a circuit pattern drawn on a reticle (i.e., a mask) onto a wafer or the like using a projection optical system, thereby transferring the circuit pattern on the wafer or the like. In a step-and-scan type exposure device (i.e., a scanner), the reticle and the wafer are relatively scanned such that an exposed area has a square slit shape and a substrate is exposed to light. In the scanner, while exposing the wafer to light, a position of a surface of a region, that is not presently exposed to light but is exposed to light later, is measured. By using the measurement result, when the region is exposed to light, the position of the surface of the region is corrected so as to be matched to an optimum exposed and image-forming position. Specifically, in a lengthwise direction of an exposure slit (i.e., a direction vertical to the scanning direction), there are a plurality of measurement points in the exposure slit region in order to measure not only a height (i.e., focus) of the position of the front surface of the wafer but also a inclination (i.e., tilt) of the front surface of the wafer.
U.S. Pat. No. 6,249,351 and US Patent Application Publication No. 2007-0086013 discuss an example of a method for measuring the focus and the tilt using an optical sensor. In the measuring apparatus discussed in the U.S. Pat. No. 6,249,351, white light from a light source is split into two light fluxes using a beam splitter and then the split light fluxes obliquely enter the subject surface and a reference surface, respectively. Subsequently, the subject light and the reference light reflected by the subject surface and a reference surface, respectively, are superimposed using the beam splitter and thereafter, a peak position is detected with respect to a white light interference signal acquired by an image sensor and measure the position of the front surface of the detection object.
As details are described below, Japanese Patent Laid-open Publication No. 07-104647 discusses an example of a typical adjustment of a light path of each of the reference light and the subject light in which an adjustment unit including mirrors and prisms are used.
In the measuring apparatus discussed in the U.S. Pat. No. 6,249,351 and US Patent Application Publication No. 2007-0086013, white light having low coherence is used. Accordingly, in a case where shifting occurs in a relative position between the reference light and the subject light on the light receiving surface of the sensor (i.e., a cross section of an optical axis of the light flux) or in a case where an optical path length of the reference light differs from that of the subject light, a measurement accuracy is degraded. This is because, a contrast of coherent light (i.e., a detected signal of the sensor) is degraded or symmetry of the coherent light collapses. Therefore, adjusting both of the relative position between the reference light and the subject light and an optical path length difference therebetween in an optical axis direction is material.
In the oblique-incidence type interferometer discussed in the specification of the U.S. Pat. No. 6,249,351, adjustment is performed such that the detection object and a reference mirrors are scanned in a Z direction in order to adjust the relative position between the reference light and the subject light and the optical path length difference therebetween. However, both of the relative position between the reference light and the subject light and the optical path length difference therebetween change according to the scanning of the detection object and the reference mirrors in the Z direction, so that, if one of the relative position and the optical path length difference is adjusted, shifting occurs in the other one. Therefore, it is hard to accurately adjust both of the relative position and the optical path length difference at the same time.
In the interferometer discussed in the specification of the US Patent Application Publication No. 2007-0086013, a plurality of mirrors are scanned in a direction vertical to a surface, thereby adjusting the optical path length difference between the reference light and the subject light. However, in a case where the plurality of mirrors is scanned, both of the relative position between the reference light and the subject light and optical path length difference therebetween change concurrently. Accordingly, if the optical path length difference between the reference light and the subject light are adjusted, shifting occurs in the relative position. Therefore, accurate adjustment of both of the above is difficult.
A hologram forming apparatus discussed in the Japanese Patent Laid-open No. 07-104647 includes an optical path length adjustment unit including two pairs of combined mirrors having angles of aperture of 90 degrees and 270 degrees, respectively. In the optical path length adjustment unit, by adjusting a relative distance between the two pairs of combined mirrors, only the optical path length difference is adjusted. More specifically, adjustment of the relative position between the reference light and the subject light is not discussed therein.